The present invention relates generally to a method and apparatus for testing a steering column assembly. More specifically, the present invention relates to an improved method and apparatus for testing the energy absorption of a steering column assembly in a simulated frontal crash.
Many modifications aimed at increasing vehicle safety have been introduced over the years. In many cases these modifications were first introduced by one vehicle manufacturer, but were later required by law under the Federal Motor Vehicle Safety Standards (FMVSS) to improve vehicle safety. Currently, these standards apply to all vehicles sold in the United States.
There are three main categories of standards that apply to cars, those numbered in the 100""s apply to crash avoidance, those numbered in the 200""s apply to occupant protection, given that a crash occurs, and those numbered in the 300""s apply to the immediate post crash considerations. The National Traffic and Motor Vehicle Safety Act of 1966 directed that all vehicles manufactured in 1968 or later satisfy a number of these standards; additional standards continue to be added.
The largest fatality reductions have been achieved from the combined effects of FMVSS 203 and FMVSS 204. FMVSS 203 requires energy absorbing steering columns to cushion the driver""s chest impact in a frontal crash. FMVSS 204 requires limited rearward displacement of the steering wheel toward the driver. The present application is specifically concerned with testing of the FMVSS 203 standard.
FMVSS 203 the standard for energy absorbing steering columns is stated in 49 CFR 571.203. The standard requires the method of testing as described in SAE J944 JUN80 be followed to show compliance. In the J944 test, the steering column assembly instrumented with a 5-axis load cell, is mounted to a test fixture. A block of wood or other soft material, representing a human body, is discharged at a specific speed toward the steering column assembly. The contact of the block with the steering wheel element attached to the steering column produces an impact similar to a frontal crash. The energy absorption of the steering column is calculated using the data collected from the 5-axis load cell.
Although specific testing methods have been noted under the FMVSS 203, other testing methods have been developed to approximate the FMVSS tests while utilizing more efficient or reproducible tests. In particular a drop tower test has been developed to improve reproducibility. In the drop tower test, the steering column assembly is instrumented with a 5-axis load cell and a hemispherical element is mounted to the steering column shaft. The steering column assembly is mounted to the crosshead of a drop tower. The crosshead is raised to a height that will result in the assembly to obtaining a specified velocity at the point of impact. The contact of the hemispherical element attached to the steering column with the ground produces an impact similar to a frontal crash.
Although present testing methods have proven acceptable, each method has drawbacks. In tests where the column is impacted with another body, there are several concerns. First, the impact issuance of the allowed claims, and hereby preserve the right to again pursue the rejected claims in a continuation application.
Additionally, in the two testing methods described above, the energy absorbed by the steering column is calculated through the use of a 5-axis load sensor. These sensors, while commonly used, have inherent problems. First, the sensors separately measure components of force and components of moment. These components must then be combined to calculate the overall energy absorbed by the shaft using complex equations. Second, each load cell costs around $5000 each and are relatively fragile. Due to the dynamics of impact testing, the cells are often permanently damaged due to their fragility. As such, the cost of impact testing with 5-axis load sensors is high.
Next, the versatility of testing set-ups for the steering column assembly is also paramount. Since the steering column assembly is composed of several different sub-assemblies, each sub-assembly must be able to be tested individually. The present testing methods do not allow for simple conversions between testing set-ups for each of the sub-assemblies.
Another drawback to the present testing method is that impact testing does not allow high-speed cameras at any location around the steering column assembly. Unobstructed positioning of the camera allows capture of every part of the column as it collapses, providing more information on each test.
Lastly, another drawback of the current tests as described above is the correlation with actual vehicle tests. The tests as described above, do not resemble the Delta V, change in velocity, pulse of an actual vehicle crash test. In an actual vehicle crash test the Delta V pulse resembles a sinusoidal shape. In the current tests, the Delta V pulse has a triangular shape with very steep deceleration.
While many attempts have been made to develop a method and apparatus to test the amount of energy absorbed by a steering column, the variations in test accuracy, test repeatability, test versatility, test correlation, data acquisition and camera coverage have exposed the limitations of each known design. Thus, it remains desirable in the art to provide a method and apparatus of testing which overcomes all of these limitations.
It is a general object of the present invention to provide an improved method and apparatus for testing automobile components wherein the energy absorbed by the component is obtained through the rapid deceleration of the component having a mass element attached to one end.
It is another object of the present invention to provide an improved method and apparatus for testing the energy absorbed by an automobile steering column. The method including the steps of mounting the steering column to a fixture, attaching a mass element to the shaft of the steering column and rapidly decelerating the fixture to approximate a frontal crash.
In one form, the present invention provides an improved method and apparatus of testing the energy absorbed by an automobile steering column in a frontal crash. The method including the steps of mounting the steering column assembly to a fixture, attaching a mass element to an end of the steering column assembly, accelerating the fixture at a specified rate and determining the force produced on the steering column assembly at specified times.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from a reading of the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.